So I've been having this unusual issue the last few weeks. For the last 100k miles the S2000 has never overheated or gone above 3 bars here in Phoenix, AZ. Yet in the last few weeks it will hit 4,5 and sometimes briefly 6 bars on many occasions. There appears to be no consistency to when it happens. Sometimes I can start the car and drive 50 miles with it never going over 3 bars... other times it will shoot right to 5 bars in the first minute and then backoff to 3 bars for the rest of the trip. Today on a 50 mile trip it was fine for the first 40 miles and then on the last 10 miles shot up from the usual 3 to 6 bars quite quickly and then settled back down to 3 bars within a few miles. When I pull over during these near overheats I do not witness any bubbling or the such from the overflow resivoir like I would expect... instead it looks perfectly normal. I have never changed the thermostat or radiator fluid and I just hit 100k miles. I know both should be done soon. Will simply doing that fix my issue or does it sound like we have something else going on here? Thanks in advance

 

Since it is relatively cheap and easy, I'd change the thermostat and flush the coolant making sure to bleed it properly and give it a try. If that doesn't work, I'd look into the water pump.

Does you heater blow hot?

 

Thanks! Not sure... to be honest I rarely if ever use the heat so I'll try it and see. Am I looking to see if it blows hot during these periods of overheating or just in general?

 

If your thermostat is in working order your heater should blow hot when the coolant is up to temp. Try touching your lower rad hose & see if it is cold (it shouldn't be)

 

How about checking the coolant level in the radiator?? Much cheaper and easier than guesswork. .

This should be step one.

No reason to flush or touch the thermostat.

Heat should be very hot always once the car is warmed up.

 

Check coolant level. To me seems like the direction may lead you to the ect (coolant temp sensor). Would inspect harness to sensor, disconnect the sensor see if your gauge changes, or you can also perform the "wiggle" test on the harness which is just moving the harness around looking for poor electrical connection within the wires.

 

Thanks for the advise everyone. Will be starting with the easiest stuff and going from there. Tonight when I drove it home it was obvious it was going to overheat at it hit bar 4...which reminded me to try the turning on the heat test. Well it was luke warm at most...this was about 5 minutes after starting the car. The car then climbed to 6 bars and it was still luke warm coming out of the vents with the heat on full. The vents suddenly started blowing very hot and the temperature went back down to 3 bars where it remained for the rest of the trip. What does this sound like? To me it sounds like my thermostat isn't opening properly or at the right times but I'm just guessing here... Will be topping off radiator fluid tomorrow if I get a chance.

 

Sounds like you got air in the coolant system. Maybe because of low fluid level, you haven't checked that yet?
You really shouldn't drive your car like this, it could easily damage your engine.

 

X2 on no driving. You'll toast your motor if you haven't already. There are two really recent overheating threads in the "under the hood section" that go through what you need to do. they all have warnings of no driving until it is resolved.

 

https://www.s2ki.com/s2000/index.php...-Advice-needed